These undefined references should be defined in the libncarg_c.a
library. So either this library didn't get built to completion, or
else NCAR Graphics was built with an option telling the Fortran
compiler not to append underscores at the end of routine names (while
at the same time the NGCALLF macro was set up to expect the
underscores).

Did you change the $NCARG/config/LINUX file and add any compile
options that might affect how Fortran routine names are compiled into
the library?

Also, can you type:

nm /usr/lib/libncarg_c.a

and email me the output.

Also, and this is just an FYI, it is cleaner to link in libraries
using the "-l" option rather than the full path to the library:

gcc -o ncarg ncarg.c -lngmath -lncarg_c -lncarg_gks -lncarg -lg2c

If your compiler can't find the NCAR Graphics libraries and/or the g2c
library, then you may need to "help" it with the -L option: